The application claims priority from Japanese Patent Application No. 2001-260995 filed on Aug. 30, 2001.
The present invention relates to a method for preparing a polyether polyol copolymer, in particular, a polyether polyol having repeating units of group: O(CH2)x as an essential structural unit of the copolymer, which permits the control of the content of the repeating units: O(CH2)x present on the copolymer so that it falls within a desired range.
Polyether polyol is a polyether glycol having hydroxyl groups on the both sides thereof and is in general prepared through the ring-opening polymerization of a cyclic ether. In this respect, there has been investigated a method for preparing a variety of polyether polyols comprising the step of copolymerizing cyclic ethers and diols in order to improve physical properties of such polyether polyols.
When a polyether polyol copolymer is prepared by copolymerizing a specific cyclic ether and a specific diol, a specific polyether polyol whose content of oxy-polymethylene repeating units (O(CH2)x repeating units) falls within a desired range can be prepared by carrying out the foregoing copolymerization, while properly designing the resulting copolymer such that the content of the oxy-polymethylene repeating units, observed when the cyclic ether is opened, is adjusted to an intended range. In this case, however, it is impossible to adjust the molecular weight of the polyether polyol copolymer derived from the cyclic ether and diol to a desired range. On the other hand, if the molecular weight of the polyether polyol copolymer is controlled to a desired range, the content of the oxy-polymethylene repeating units present in the polyether polyol copolymer cannot be adjusted so as to fall within a desired range.
Among the polyether glycols having hydroxyl groups on the both sides thereof, particularly industrially significant ones are poly(tetramethylene ether) glycols (hereunder referred to as xe2x80x9cPTMEGxe2x80x9d) prepared through the ring-opening polymerization of tetrahydrofuran (hereunder referred to as xe2x80x9cTHFxe2x80x9d). This PTMEG possesses oxy-tetramethylene repeating units and has widely been used as a material for elastic materials used in, for instance, spandex, synthetic leather and optical fibers. However, an elastomer derived from the PTMEG, in particular, that having a high molecular weight is quite susceptible to crystallization at a low temperature or during storage over a long period of time and it suffers from various problems such that physical properties thereof at a low temperature are insufficient and that the physical properties thereof deviate from the desired ones or the designed ones, during storage.
As a means for solving these problems, there has been proposed a method, which makes use of a copolymerized PTMEG obtained by the copolymerization of THF with other cyclic ethers instead of a PTMEG as a homopolymer of THF. In this method, the regularity in the arrangement of the resulting molecule is put into disorder, if THF and other cyclic ethers are copolymerized to thus reduce the crystallinity of the resulting copolymer molecules. For instance, there have been disclosed a copolymerized PTMEG of THF and 3-methyloxetane in Japanese Examined Patent Publication (hereunder referred to as xe2x80x9cJ. P. KOKOKUxe2x80x9d) No. Hei 4-20013; and a copolymerized PTMEG of THF and 3-alkyltetrahydrofuran in J.P. KOKOKU No. Hei 7-116276. However, these methods, which make use of such ring-opening copolymerization, require the use of cyclic ether compounds other than THF as copolymerizable components. For this reason, these methods suffer from problems in that the kinds of cyclic ethers used in such copolymerization are considerably limited because of the difficulty of preparing cyclic ether compounds and that the production cost of the cyclic ether is liable to be high as compared with that required for the preparation of polyols.
As another method for synthesizing a copolymerized PTMEG there has been known one, which makes use of glycols as components to be copolymerized with THF instead of cyclic ethers. Various kinds of glycols have been known and glycols are cheaper than the cyclic ethers and therefore, the use of glycols may extend the tolerance in the molecular design of such a copolymerized PTMEG. More specifically, J.P. KOKOKU No. Hei 7-13139 discloses a method for preparing a polyether polyol from THF and a glycol in the presence of a hetero-polyacid, as a catalyst, which contains at most 15 water molecules coordinated thereto or present therein.
On the other hand, when using a copolymerized PTMEG as a material for elastomers, it is quite important to control the ratio of copolymerizable components other than THF. If the ratio of such a copolymerizable component is low, the PTMEG is still strongly susceptible to crystallization and accordingly, the resulting elastomer is insufficient in the improvement of the intended low temperature properties and storage stability. On the other hand, if the ratio of such a copolymerizable component is high, the low temperature properties and storage stability of the resulting elastomer can be improved, but other physical properties are greatly influenced and the tensile strength thereof may, for instance, be extremely reduced.
When preparing a copolymerized PTMEG having an intended molecular weight by copolymerizing THF and a glycol, however, the charged mass ratio of the THF to the glycol is unconditionally determined and therefore, the ratio of the oxy-tetramethylene repeating units present in the resulting copolymerized PTMEG is also constant. In other words, when copolymerizing THF and a glycol, a copolymer having a desired content of oxy-tetramethylene repeating units can be prepared by carrying out the copolymerization in such a manner that the content of oxy-tetramethylene repeating units resulted from the ring-opening of the THF is equal to that of the designed copolymer, but the molecular weight of the copolymerized PTMEG derived from THF and a glycol is not in agreement with that of designed copolymer. On the other hand, if the molecular weight of the copolymerized PTMEG is controlled to a desired level, the content of the oxy-polymethylene repeating units present in the resulting copolymer cannot be adjusted so as to fall within a desired range. This phenomenon is also observed in the case disclosed in J.P. KOKOKU No. Hei 7-13139 and any copolymerized PTMEG whose content of oxy-tetramethylene repeating units and molecular weight were simultaneously changed or controlled could not be prepared.
On the other hand, even in case where cyclic ethers other than THF are used, a material having desired physical properties can easily be prepared if the content of the oxyalkylene repeating units derived from a cyclic ether and the molecular weight can simultaneously be controlled in the resulting polyether polyol copolymer. However, there has not yet been proposed any such a technique.
Accordingly, it is an object of the present invention to provide a method for preparing a polyether polyol copolymer suitably used as an elastomer material, which can arbitrarily change the content of O(CH2)x units present in the main chain of the copolymer and can simultaneously control the molecular weight thereof so that the resulting copolymer has an appropriate crystallizability.
The inventors of this invention have conducted various studies to achieve the foregoing object, have found that the foregoing problems associated with the conventional techniques can effectively be eliminated by the simultaneous use of a specific cyclic ether and a diol having a structure similar to that obtained by ring-opening the cyclic ether when copolymerizing the specific cyclic ether with other polyols in the presence of an acid catalyst to thus give a polyether polyol copolymer having O(CH2)x repeating units as essential structural units and have thus completed the present invention.
According to a first aspect of the present invention, there is provided a method for preparing a polyether polyol copolymer comprising the step of copolymerizing (1) a cyclic ether represented by the following formula (I): 
wherein x is an integer ranging from 2 to 10; (2) a diol represented by the following formula (II):
HOxe2x80x94(CH2)xxe2x80x94OHxe2x80x83xe2x80x83(II)
wherein x is the same as that specified above; and (3) other polyols, in the presence of an acid catalyst.
According to a second aspect of the present invention, there is provided a method for preparing a polyether polyol comprising the step of copolymerizing (1) tetrahydrofuran, (2) 1,4-butanediol and (3) other polyols, in the presence of an acid catalyst.
According to a third aspect of the present invention, there is provided the use of a combination of the foregoing cyclic ether represented by Formula (I) and the diol represented by Formula (II) in the method for preparing a polyether polyol, in order to adjust the content of O(CH2)x units present in the O(CH2)x unit-containing polyether polyol copolymer.
According to a fourth aspect of the present invention, there is provided the use of a combination of tetrahydrofuran and 1,4-butanediol in the method for preparing a polyether polyol, in order to adjust the content of O(CH2)x units present in the O(CH2)x unit-containing polyether polyol copolymer.